This invention relates to illumination systems of the type employing a light source and a reflector coaxially mounted along a central axis of the illumination system for reflecting light, which emanates radially outward from an arc of the light source, generally along the central axis to a utilization device.
Prior art illumination systems of the foregoing type employing light sources, such as mercury or xenon lamps of the short arc type, and elliptical reflectors are commonly used in the semiconductor industry to illuminate light integrators used with such illumination systems or other such utilization devices. However, these illumination systems are not capable of efficiently imaging reflected light from the elliptical reflector at the utilization device because the magnification of the arc of the light sources varies significantly in the azimuthal direction across the curved surface of the elliptical reflector so that the field size of the image of the arc also varies significantly at the utilization device.
It is the principal object of this invention to provide an improved illumination system of the same general type for more efficiently imaging the reflected light at the utilization device.
This object is accomplished in accordance with the illustrated preferred embodiment of the present invention by employing a light source, such as a mercury or xenon lamp of the short arc or capillary type, mounted along a central axis of the illumination system to emit light radially outward from an arc disposed on the central axis, and by further employing a conical reflector and a toroidal lens coaxially mounted about the central axis to direct light, which emanates radially outward from the arc of the light source, symmetrically about the central axis to a utilization device. The conical reflector and the toroidal lens provide a substantially constant magnification of the arc of the light source and concomitantly a substantially constant field size of the image of the arc that may be matched to the input port of the utilization device.